184 



THE AMEKICAN MONTHLY 



[October, 



maintained through many successive 

 generations. 



By means of these pure cultures 

 we are enabled to study the modify- 

 ing influences of environment upon 

 form or function, the influence upon 

 growth and reproduction of various 

 chemical substances, of different de- 

 grees of temperature, etc. 



It is only necessary to mention the 

 brilliant discoveries of Pasteur and of 

 Koch relating to the role of these 

 minute plants in various processes of 

 decomposition and in the etiology of 

 infectious diseases, in order to call 

 attention to the practical results which 

 these researches promise. 



Without doubt the very great ac- 

 cessions to our knowledge in this 

 direction which have been made dur- 

 ing the past few years are largely due 

 to improvements in technique relating 

 to the recognition (by staining re- 

 agents, special modes of illumination, 

 etc.) and cultivation of the micro- 

 organisms in question. 



In a paper read at the Cincinnati 

 meeting of this Association, in 1881, 

 a detailed account was given of the 

 writer's method of conducting culture 

 experiments. Further experience has 

 fully confirmed my conviction that 

 the method referred to has advantages 

 over all others for cultivating micro- 

 organisms in fluid media, and my ob- 

 ject at present is to give a practical 

 demonstration by which the advan- 

 tages claimed will be made apparent, 

 rather than to add anything to the 

 technical account of my mode of op- 

 erating. At the same time I shall 

 call attention to the invaluable method 

 of surface cultivation, which is so 

 highly recommended by Koch, and 

 which has been published by him 

 since the reading of my paper above 

 referred to. 



The special advantages of each 

 method will be pointed out, not with 

 a vie^v to showing that one is superior 

 to the other, but in order to indicate 

 the particular cases in which one or 

 the other is preferable, for neither can 

 entirely take the place of the other ; 



and if a pure culture may be more 

 easily maintained in an hermetically 

 sealed flask, it is unquestionably true 

 that the method of Koch has added 

 greatly to our resources for the isola- 

 tion and naked-eye recognition of the 

 innumei'able species of bacteria which 

 surround us on every side, which in- 

 fest the water we drink, the air we 

 breathe, and, as harmless parasites, 

 the human mouth and intestine in 

 countless hosts and of many different 

 forms. 



It is onl}' by resorting to some 

 method by which we are able to se- 

 cure and maintain ' pure cultures ' 

 that we are able to obtain a precise 

 knowledge of this extensive micro- 

 scopic flora, for in nature the species 

 are mingled together in such a way 

 that nothing but confusion and uncer- 

 tainty can come from the attempt to 

 establish species upon morphological 

 characters alone. 



There is nothing novel in the form 

 or construction of the little flasks 

 which are used in the method which 

 I recommend to you. They have, no 

 doubt, been used occasionally b}- other 

 experimenters for various purposes 

 prior to my calling attention to their 

 special advantages for the purpose in 

 view. These advantages are best se- 

 cured by making the flasks of mod- 

 erate size, and by drawing out the 

 neck into a slender capillary tube, so 

 that the mode of manipulation which 

 I shall demonstrate becomes practi- 

 cable. The method, taken as a 

 whole, is oi'iginal, and, so far as I 

 know, had not been practised by any 

 one prior to the publication of my 

 paper referred to. The usual method 

 has been to use open-mouthed flasks 

 or test-tubes, into which a sterilized 

 culture-fluid is introduced, and from 

 which atmospheric germs are exclu- 

 ded by a sterilized plug of cotton- 

 wool. In skilful hands this method 

 gives satisfactory results, but it re- 

 quires much time and care, and the 

 most experienced manipulators can- 

 not avoid the occasional contamina- 

 tion of a culture, or the 'breaking 



